I'm a visual learner, so I tried to make a map of the changes as I understand them... (feel free to point out where I'm wrong or if anyone has any first hand knowledge.)
The
purple box is where the elevator up to the future Metropolitan Lounge is located.
The
red boxed area (the main waiting room) will be closed from 1-4am (along with the historic ticketing area, which is not currently open to the public.)
The
green boxed area (the seating area in concourse) will remain open to Amtrak passengers during the overnight hours.
The
blue line is the path passengers will take from West (Alameda) entrance to the waiting area in the concourse. It also maintains access to the tunnel under the train tracks, the portal to the Red/Purple Line station, Amtrak ticketing and Amtrak bus area.
If this is the how the station works... the overnight situation sounds like a good compromise. It closes off a large portion of the historic waiting room, which should make it easier for security to control who is in the station during the overnight hours. But it still maintains an area for passengers to wait and access to the major services at the station (and both patios!)
Tip of the hat to LOSSAN for their awesome Union Station Map, check out their awesome brochure
here.
Oh, and please excuse my mediocre Photoshop skills.